This invention relates to techniques to locate transition zones in a multi-alloy metal forging. A transition zone is a boundary region in a forging between one metal alloy composition and another met al alloy composition. In particular, the invention relates to measuring the location of a transition zone in a forging using ultrasonic waves.
Using multiple alloys in a forging allows the forged component to have different material properties at different locations of the forging. Forged components are often formed to have material properties, e.g., strength and heat resistance, that vary throughout the component. Incorporating multiple alloys in a forging is one technique to vary the material properties in a forged component.
The use of multiple-alloys raises concerns regarding thermal distortions among the different alloys in a forging. Each of the different alloys in a multiple alloy forging may have different thermal expansion and contraction characteristics. To control the thermal expansion and distortion between zones of different alloys, the transition zone is positioned to avoid undue thermal distortions caused by differences in the coefficients of thermal expansion among the different alloys in the forging.
The location of the transition zone between the alloys in the component is measured as part of a determination to predict the amount of distortion that a forged component will experience at different temperatures. A nondestructive technique is needed to locate transition zones in a forging to, for example, perform a thermal distortion analysis of the forging.
Conventional methods for locating a transition zone include chemical analysis of the surface of the forging. The internal location of the transition zone is estimated based on the surface data obtained from the chemical analysis and prior knowledge of the shape of the transition zone. This chemical method assumes that the transition zone has a constant shape in each forged component. However, the shape of a transition zone tends to vary from component to component. The chemical method can be inaccurate in determining the position of a transition zone because of variances in the shapes of the zone. A more accurate measurement technique is needed to locate a transition zone.
Ultrasonic measurements of forgings have not been used to measure the location of transition zones. Ultrasonic measurements have been used to monitor the quality of bonds in composite structures. The reflection of ultrasonic waves passing through a forged component is monitored to determine the quality of the bond by detecting porosity or delamination-type defects in the component. In ultrasound bond quality applications, the location of the material interface is known and measurements are not made to locate a transition zone.
Further, ultrasonic thickness gauges are available to measure the thickness of materials. These gauges generally require an easily identifiable and strong ultrasound echo signal, e.g., a backwall ultrasound echo signal, to measure the signal travel time through the material. Transition zones do not provide an easily identifiable signal source for existing ultrasound thickness gauges to analyze and measure. Ultrasonic thickness gauges are not applicable to locating a transition zone in a multiple alloy forging because there is no easily identifiable echo from the transition zone region between alloys.
Ultrasonic beam attenuation and scattering techniques have been used to estimate grain size in forged materials. These attenuation and scattering techniques focus an ultrasonic beam to reduce the scattering from grains in materials. Prior ultrasonic techniques associated with grain scattering primarily relate to the elimination of scattering noise to improve inspection sensitivity. These techniques have not been applied to locate transition zones.
There is a long felt need to identify and measure the location of alloy to alloy transition zones in a multiple alloy forging. The method should be non-destructive and should measure transition zones below the surface of a forged component. It would be helpful if the method used readily available equipment so that the method can easily be implemented in the production of forgings.
In a first embodiment, the invention is a method to determine a depth of an internal feature in a forging using an ultrasonic transducer comprising: collecting data on echoes reflected by the internal feature of ultrasonic signals transmitted into the forging;
correcting the collected data to compensate for attenuation of the echoes and signals in the forging; and determining the depth of the internal feature.
In a second embodiment, the invention is a method to determine a depth of an internal feature in a forging having a generally circular cross section using an ultrasonic transducer comprising: collecting data on echoes reflected by the internal feature of ultrasonic signals transmitted into the forging, wherein the data is collected at a plurality of angular positions around a perimeter of the forging; correcting the collected data to compensate for attenuation of the echoes and signals in the forging; partitioning the data to eliminate data corresponding to echoes from surfaces of the forging; identifying a maximum amplitude signal from the partitioned data for each of the angular positions; plotting the maximum amplitude signal data on polar chart and identifying a center of the maximum amplitude signal data, and plotting a circular cross-section of a transition zone coaxial with the center and a radius corresponding to an average value of the maximum amplitude signal data.
In a third embodiment, the invention is a system to determine a depth of an internal feature in a forging comprising: an ultrasonic transducer positioned on a surface of the forging, wherein said transducer transmits ultrasound beams into the forging, receives echoes reflected from internal feature in the forging and generates data signals indicative of the echoes, and a computer receiving the data from the transducer, wherein said computer executes a program to process said data by correcting the data to compensate for attenuation of the echoes and signals in the forging and to determine a depth of the internal feature in the forging.